Remove -fPIC flag from build system.
Remove -fPIC flag from build system.

This remove the `-fPIC` flag, indicating position independant code
generation, from the build system.

Citing GCC's official code generation docs:

> This option makes a difference on the m68k, PowerPC and SPARC.

We do not support any of these architectures, so remove the flag!

References:

- https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options

yuryleb/osrm-backend,hydrays/osrm-backend,hydrays/osrm-backend,beemogmbh/osrm-backend,felixguendling/osrm-backend,oxidase/osrm-backend,KnockSoftware/osrm-backend,raymond0/osrm-backend,yuryleb/osrm-backend,frodrigo/osrm-backend,raymond0/osrm-backend,Project-OSRM/osrm-backend,deniskoronchik/osrm-backend,oxidase/osrm-backend,deniskoronchik/osrm-backend,yuryleb/osrm-backend,Project-OSRM/osrm-backend,bjtaylor1/osrm-backend,oxidase/osrm-backend,beemogmbh/osrm-backend,deniskoronchik/osrm-backend,oxidase/osrm-backend,neilbu/osrm-backend,beemogmbh/osrm-backend,felixguendling/osrm-backend,neilbu/osrm-backend,frodrigo/osrm-backend,deniskoronchik/osrm-backend,KnockSoftware/osrm-backend,KnockSoftware/osrm-backend,bjtaylor1/osrm-backend,duizendnegen/osrm-backend,raymond0/osrm-backend,Project-OSRM/osrm-backend,neilbu/osrm-backend,frodrigo/osrm-backend,raymond0/osrm-backend,yuryleb/osrm-backend,bjtaylor1/osrm-backend,Project-OSRM/osrm-backend,arnekaiser/osrm-backend,bjtaylor1/osrm-backend,duizendnegen/osrm-backend,frodrigo/osrm-backend,arnekaiser/osrm-backend,hydrays/osrm-backend,hydrays/osrm-backend,KnockSoftware/osrm-backend,duizendnegen/osrm-backend,arnekaiser/osrm-backend,beemogmbh/osrm-backend,duizendnegen/osrm-backend,neilbu/osrm-backend,arnekaiser/osrm-backend,felixguendling/osrm-backend